Cervical stenosis with spinal cord compression and consequent myelopathy is a very common problem encountered by the spine surgeon. The usual cause of multilevel cervical stenosis is spondylosis and/or ossification of the posterior longitudinal ligament. Surgical decompression either through an anterior or posterior approach can be undertaken.
An anterior approach usually involves multilevel corpectomy with fusion and stabilization. The main drawback of this technique is the increased time and complexity of the procedure as well as the risk of pseudoarthrosis and accelerated degeneration at the levels above and below the fusion.
A posterior approach has traditionally involved a simple laminectomy, laminectomy with facet fusion, or more recently laminoplasty. The drawback of a simple laminectomy is the risk of late clinical deterioration form either kyphosis or postlaminectomy scar formation. Laminectomy with facet fusion decreases the risk of kyphosis but it also decreases the range of motion in the spine and increases the risk of accelerated degeneration at the levels above and below the fusion.
Laminoplasty either through open door or double door technique developed more recently provides greater stability and range of motion when compared with laminectomy alone. This technique entails laminoplasty for decompression with laminar fusion with allo- or autograft bone and/or fixation with a plate. The principle behind laminar fusion and fixation is that it maintains the decompression following laminoplasty as well as the displaced lamina in a fixed position thereby providing stabilization also.
U.S. Pat. No. 6,080,157 to Cathro et al. describes an implant to stabilize the lamina after an open door laminoplasty technique. A major limitation of this implant and technique is that a single implant extends to all the laminoplasty levels and does not provide well for lamina fusion, thereby being susceptible to stress fatigue. U.S. Pat. No. 5,980,572 to Kim et al. describes an implant to stabilize the lamina after a double door laminoplasty technique. This implant also does not provide well for lamina fusion and is susceptible to stress fatigue. U.S. patent application Ser. No. 10/035,281, filed by the author, describes several laminar fixation plates with and without a bone spacer that allow for lamina fixation and fusion.
The present invention is an apparatus for use in either the open door or double door laminoplasty technique to fuse and stabilize the lamina in the spine thereby preserving the range of motion as well as maintaining stability.
The present invention relates a laminar fusion and fixation system following either open door or double door laminoplasty technique. This system with the bone fusion spacer and plate reduces surgical time and simplifies laminar fusion and fixation after laminoplasty.
The lamina fixation device consists of a plate contoured at each end with a hollow spacer in the middle with variable length but uniform width and thickness specific for the cervical, thoracic or lumbar spine. The contoured design of the plate allows screw placement in the lamina or spinous process on one side and the facet on the other side. The spacer edges can be straight or contoured with a notch to allow securement to the lamina on one side and the lateral mass or facet on the other side. This implant is made of titanium or similar alloy with magnetic resonance imaging compatibility. The hollow spacer can be packed with allograft or autograft bone to provide for lamina fusion. Alternatively, the implant can be made of allograft bone or hydroxyapatite or similar absorbable material.
In another embodiment, the lamina fixation device is a plate and spacer construct designed for laminar fusion and fixation following double door laminoplasty. The hollow spacer in the middle of the plate allows for laminar fusion in the decompressed position once packed with either allograft bone, autograft bone, or bone morphogenic protein and with the plate design bent on either end securing the graft to the lamina and/or the facets on both sides.
The procedure as would be undertaken with the use of the laminoplasty fixation system is described as follows. An open door laminoplasty entails creating a gutter at the junction of the lamina and medial aspect of the facet on both sides with the use of a drill. On the side of the laminoplasty opening, the drilling is carried through into the canal or the opening completed with a small kerrison rongeur. At the other side, the inner cortex at the lamina and facet junction is not drilled. The lamina at the open end is elevated and the spinous process pushed away in order to create a greenstick osteotomy and allow for the laminoplasty decompression. Typically, at least one centimeter of distraction between the lamina and the facet provides for a good spinal decompression. In order to maintain the position of the lamina, the pre-contoured laminar fixation plate/spacer construct of appropriate size is positioned between the lamina and the facet. The spacer maintains the displaced position of the lamina and the plates with the contoured ends secure the construct via screws to the lamina and facet.
Another variation on the open door laminoplasty is the expansive laminoplasty most suited for the thoracolumbar spine. In this method, the lamina on either side at the junction of the facets are drilled and opened. A lateral spinal canal recess decompression and/or foraminotomy is undertaken and the lamina replaced with the spacer/plate construct on both sides.
A double door laminoplasty is created by drilling on each side at the laminar and facet junction the outer laminar cortex and sparing the inner laminar cortex. The spinous process is resected and a midline gutter is also created which extends through the inner cortex which can be opened with a small kerrison rongeur. The lamina on either side are lifted and opened creating a greenstick osteotomy on each side. In order to maintain the decompressed position of the lamina, the spacer/plate construct is placed. The plate can either be fixated with screws to the lamina or the facets on both sides